A container which has been conventionally used for dispensing viscous materials such as pasty products or the like is disclosed in U.S. Pat. No. 3,361,305. Such conventional dispensing containers generally include a container body having a cylindrical shape provided at the upper portion thereof with a nozzle and a pump chamber which, in turn, is provided with an elastically compressed valve. These dispensing containers also include a piston displaceably assembled in the container body so as to force the contents toward the nozzle and then out therethrough by action of the pump chamber.
In conventional dispensing containers constructed in this fashion, the container body must be lightly sealed in order to satisfactorily ensure the pumping action of the pump. Therefore, after the container body is charged with a pasty material, the piston is inserted into the container body through the charging end thereof and is guided along the inner surface through, for example, seal lip means, as it advances for dispensing the contents from the container. Such construction does not permit the gas or air within the container to escape to the exterior of the container when the piston is inserted in the charging end of the container body and causes an increase in the frictional resistance between the periphery of the piston and the inner surface of the container body, thus resulting in extreme difficulty in inserting the piston into the container body. This leads to a failure in the manufacturing of the dispensing container at high speeds, thereby limiting productivity.
In order to avoid such problems, a structure has been proposed which facilitates the insertion of the piston into the container body. Unfortunately, there is an unsatisfactory sealing between the piston and the container body in the proposed structure which results in the volatilization of the volatile components such as water, organic solvents and the like comprising the pasty material charged into the container, thereby resulting in the substantial deterioration of the pasty product to an unserviceable degree.
In view of the forgoing, it has been proposed to roughen a part of the inner surface of the container body to permit the air between the piston and the contents charged in the container body to escape through the roughened section, as disclosed in Japanese patent application Laid-Open Publication No. 68368/1982. Unfortunately, the roughened section of the inner surface of these container bodies has been formed with even roughness and has therefore been unable to control both the speed of insertion of the piston into the container body and the discharge of air from the container body. In addition, the speed of insertion of the piston in these devices is increased to a degree sufficient to forcedly press the piston against the contents at the last stage of insertion, resulting in the leakage of the contents through the roughened surface section.
Accordingly, it would be desirable to develop a dispensing container for viscous materials, such as pasty products, having a container body into which a piston may be readily and smoothly inserted at a high speed while at the same time ensuring the seal between the piston and the container body.